In a general endoscope device, light emitted from a lamp of a light source system is guided to an endoscope tip portion by a light guide provided inside an endoscope insertion section to be inserted into a subject and is emitted through an illuminating window disposed in the endoscope tip portion, and thus, an observation site of the subject is illuminated. White light is used for observation of general organism tissues, but in recent years, an endoscope device capable of enhancing a state of a mucosal tissue through irradiation with light of a wavelength of a specific narrow band or capable of special light observation for observing autofluorescence of a fluorescent material precedently administered is utilized (Patent Documents 1 and 2). When such a type of endoscope device is used, since organism tissue is irradiated with special light, neovascular generated in a mucosal layer or a submucosal layer may be observed, and hence, a microstructure of a mucosal surface not obtained in a general observation image may be described.
In Patent Documents 1 and 2 mentioned above, merely a specific wavelength band of light emitted from a white light source such as a xenon lamp is taken out by using a color filter so as to be used as the special light. It is noted that a laser light source may be used as the white light source apart from the xenon lamp, and a light emitting apparatus for generating white light through a combination of, for example, a blue laser light source and a phosphor causing excitation emission by using a blue laser beam as excitation light has been proposed (Patent Document 3).
The endoscope device of each of Patent Documents 1 and 2, however, employs a structure in which the light emitted from the white light source is divided on a time basis by a color filter so as to frame-sequentially emit light of different wavelength bands (of, for example, R, G and B). Therefore, it is necessary to synthesize captured images of a plurality of frames (of R, G and B) for obtaining a full-color observation image, which prevents increase of the frame rate of an observation image. Furthermore, since the illumination light is generated through light absorption with the color filter, the quantity of light is unavoidably reduced, which is a factor to increase a noise component of the observation image. Although it is possible to increase the sensitivity by reducing the frame rate, a resultant image is easily blurred in this case.
On the other hand, in diagnosis with special light, tissue information of, for example, a surface layer portion or a portion toward a deep layer portion of organism tissue is a significant observation target. In regard to, for example, a cancer of a digestive organ, tumor vessels appear in a mucosal surface layer portion at an early stage, and the tumor vessels are found to expand, meander and increase in the density as compared with general blood vessels appearing in the surface layer portion. Therefore, the kind of tumor may be identified by dissecting the characters of the vessels. In the aforementioned endoscope device using a color filter, however, when tissue information of a surface layer portion of organism tissue in particular, for example, is desired to observe, it is difficult to restrict the transmission wavelength band of the color filter to a specific narrow band, and in addition, the illumination light of the restricted narrow band may not be obtained in a sufficient quantity, and therefore, the image quality of an observation image is disadvantageously degraded.